Label including amorphous tape with improved properties

ABSTRACT

A label for marking and remote identification of objects, is formed of at least one elongated tape (10) of a magneto-elastical material with a high magneto-mechanical coupling, the tape (10) being movably arranged within a cavity in the label. At least one element (11) is applied on the tape (10) for changing the mass of the tape (10), while preserving the magnetic properties of the tape. The cavity contains a liquid of low viscosity, such as silicon oil, which surrounds the tape.

FIELD OF THE INVENTION

The present invention relates to amorphous tapes with improvedproperties for use in labels. The labels are used for the purpose ofmarking and identifying objects.

DESCRIPTION OF THE PRIOR ART

The type of labels mentioned above is described in, e.g., WO 88/01427and EP-B-0 096 182. The labels in these patent specifications areprovided with an internal cavity, in which at least one tape of anamorphous material resides. The tape material has a largemagneto-mechanical coupling, i.e., a mechanical load on the tape alsocauses a change in the magnetic properties of the tape. The tape orstrip is a kind of mechanically resonating element, the resonancefrequency of which being located in different frequency bands dependingon the length of the tape.

The magnetic properties of the tape are also influenced by its lengthand geometry. For instance, the demagnetizing effect present at the endsof a tape has a substantially different influence on the magnetizationof the tape, depending on the length of the tape. This means that tapeswith different lengths are magnetized to different degrees when exposedto an identical magnetic field.

With magneto-elastical resonance elements, such as amorphous tapes, themagneto-elastical coupling factor, which affects the signal strength ofthe tape, and the Δ-E effect, which affects the resonance frequency ofthe tape, both depend on the magnetization of the tape. In theembodiment disclosed in EP-B-0 096 182, the above-mentioned factors havesubstantially no importance. In the embodiment according to WO 88/01427,on the other hand, certain problems are associated with adjusting amagnetic control field in the form of a bias field, if tapes withdifferent lengths are used together in labels, which are readsimultaneously. This is particularly true, if simultaneous signals aredesired from many tapes at the same time, and if all tapessimultaneously are supposed to produce a high coupling factor and astrong frequency response. If, for instance, such a control field isused, that optimally magnetizes tapes with shorter lengths, longer tapeswill already be over-magnetized beyond saturation. Thus, significantproblems arise when it comes to detecting the tapes and keeping thesignals within the desired part of the frequency band of the tapes. Tosome extent, the above-mentioned problem may be reduced by producing acontrol field in a considerably more complex and complicated way.However, the improvement does only occur to a minor degree, and acertain amount of time is lost at the label detection.

The label detection is done by exposing the tapes to a magneticinterference signal, whereby the tapes are forced into a state ofmechanical oscillation. The tape resonance can be detected by the use ofa magnetic detection coil. The tape resonance frequency is highlyinfluenced by surrounding magnetic fields, and the above-mentioned biasfield is used to vary the magnetic field in an interrogation zone,thereby making it possible to simultaneously detect identical tapes,which are exposed to magnetic fields of different strengths or differentdirections.

BRIEF SUMMARY OF THE INVENTION

An object with the present invention is to provide tapes, which areidentically magnetized but which work within different frequency bands.This is accomplished by the use of tapes with identical geometries(length, width and thickness), which are exposed to an influence forchanging the tape mass while preserving the magnetical properties of thetape. Functionally, these new resonance elements may be viewed upon as aspring, the spring constant of which being magnetically controllablethrough the Δ-E effect, and which has a mass applied at each end. Theresonance frequency then depends on the masses, the spring constant andthe self-mass of the spring/tape.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail by way of preferredembodiments and with reference to the accompanying drawings, in which

FIG. 1 is a schematic perspective view of a tape according to theinvention, and

FIG. 2 is a graph showing the resonance frequency of different tapes asa function of a surrounding magnetic field.

DETAILED DESCRIPTION

FIG. 1 shows an elongated tape 10, which is made of an amorphousmaterial. The material has a large magneto-mechanical coupling, whichmeans that the magnetical behaviour of the material is stronglyinfluenced by the mechanical conditions of the tape. This is true to thesame extent also inversely. At each end of the tape 10, elements 11 arearranged so as to change the mass of the tape 10. Despite the presenceof the elements 11, the magnetical properties of the tape will besubstantially preserved, hence the elements are preferably formed of anon-magnetic material. Furthermore, to avoid eddy-current losses, thematerial is preferably not electrically conducting.

The element 11 may be mounted on the tape 10 by means of gluing,clamping, geometrical locking, etc. As an alternative, the masses may bearranged by means of electrochemical deposition. The latter method issuitable for industrial scale manufacture, wherein the additional masswill be properly fixed on the tape and will easily be given a streamlineshape. By the use of this manufacturing method, it is also possible toexcite the tape to oscillation during the deposition and to measure thetape resonance frequency. Thereby, the deposition may be interrupted, assoon as the tape has reached a desired resonance frequency.

As an alternative to applying an additional mass on the tape, a localmodification of the geometry of the amorphous tape may realize a changeof mass without any significant change in the magnetical properties ofthe tape.

In order to give the tapes the ability to vibrate freely, the cavity 13in which they are mounted within the label must be larger than theextension length of the tape. To further increase the ability of thetape to oscillate without any significant limitation by mechanicalcontact with the cavity walls, the tape may be provided with apreferably centrally arranged opening. A pin 12 is arranged through theopening, thereby preventing the tape from being displaced too much inthe cavity 13, in which case its vibrating abilities would be decreased.The tapes have proven to have particularly good properties, if thecavity 13 is filled with a thin liquid 14 of low viscosity, such assilicone oil. The liquid 14 improves the possibilities for a harmonicaloscillation, without any substantial damping of these oscillations.

FIG. 2 shows the tape resonance frequency as a function of an appliedbias field or control field. The X-axis represents the magnetizing fieldintensity in Oersted, and the Y-axis represents the resonance frequencyin Hz. The uppermost graph in the FIG. 2 diagram relates to a tape, onwhich no masses are applied. The next graph relates to a tape, both endsof which being provided with an element 11 weighing 3 mg. Below thatgraph, a graph representing a tape with an applied mass of 6 mg isshown, and the last graph refers to a tape with an applied mass of 12 mgat each end of the tape. The tape dimensions in this embodiment are:length=60 mm, width=2 mm, and thickness=0.025 mm.

According to FIG. 2, every graph has a relatively linear portion betweenthe values 0.20 and 0.60 for the magnetizing field intensity H. Withinthe same portion the tape resonance frequency varies betweenapproximately 15000 Hz and 35000 Hz, providing a good opportunity toidentify many tapes in one detection process.

Furthermore, tapes with applied masses of different sizes exhibitfrequency minimum at the same magnetic field, even if the actualfrequency values deviate from each other. Correspondingly, the same istrue for the coupling factor of the tapes, which reaches its maximum atapproximately the same magnetizing field intensity H of the bias field.

I claim:
 1. Label for marking and remote identification of objects,comprising at least one elongated tape of a magneto-elastical materialwith a high magneto-mechanical coupling, the tape having a pair of longsides and a pair of short sides, the tape being movably arranged withina cavity in the label, further comprising at least one element on thetape for changing a mass of the tape, while preserving magneticalproperties of the tape, wherein the tape is surrounded in the cavity bya liquid of low viscosity.
 2. Label according to claim 1, wherein theelement is applied at one of the short sides of the tape.
 3. Labelaccording to claim 1, wherein the element is applied at each short sideof the tape.
 4. Label according to claim 1, wherein the element is madeof a non-magnetic material.
 5. Label according to claim 1, wherein theelement is made of an electrically non-conducting material.
 6. Labelaccording to claim 1, wherein the element is glued to the tape.
 7. Labelaccording to claim 1, wherein the element is electrochemically depositedon the tape.
 8. Label according to claim 1, wherein the element isclamped to the tape.